Positive photoresists containing an alkali-soluble resin and a photosensitizer such as 1,2-naphthoquinone diazide are known as resists for use in, for example, the manufacture of semiconductor devices such as ICs and LSIs, the manufacture of displays such as LCDs, and the manufacture of printing plates. One proposed positive photoresist composition contains a mixture of an m-cresol novolac resin and a p-cresol novolac resin as an alkali-soluble resin (see, for example, PTL 1).
Whereas the positive photoresist composition disclosed in PTL 1 is developed to provide high developability, e.g., high sensitivity, there is a need for a higher sensitivity because finer patterns have been used with the increasing packing density of semiconductor devices in recent years. Unfortunately, the positive photoresist composition disclosed in PTL 1 has insufficient sensitivity for use in forming such finer patterns. A need also exists for a higher heat resistance because semiconductor manufacturing processes, for example, involve various heat treatments. Unfortunately, the positive photoresist composition disclosed in PTL 1 has insufficient heat resistance.
Also proposed is a photoresist phenolic resin with high sensitivity and high heat resistance that is prepared by reacting, for example, p-cresol with an aromatic aldehyde and then adding and reacting a phenol and formaldehyde in the presence of an acid catalyst (see, for example, PTL 2). This photoresist phenolic resin has a higher heat resistance than those in the related art, although it has insufficient heat resistance to meet the high level of heat resistance required in recent years.
Also proposed is a photoresist phenolic resin with high sensitivity and high heat resistance that is prepared by reacting a phenol such as m-cresol, p-cresol, or 2,3-xylenol with an aromatic aldehyde and then adding and reacting formaldehyde in the presence of an acid catalyst (see, for example, PTL 3). This photoresist phenolic resin has a higher sensitivity than those in the related art, although it has insufficient heat resistance to meet the high level of heat resistance required in recent years.
One problem is that a novolac resin, which is an alkali-soluble resin, designed to have a higher alkali solubility so that it has a higher sensitivity exhibits a lower heat resistance, whereas a novolac resin designed to have a higher heat resistance exhibits a lower sensitivity, and this makes it difficult to achieve high sensitivity and high heat resistance at the same time at a higher level. Accordingly, there is a need for a material that has high sensitivity and high heat resistance at the same time at a higher level.